Produced fluids coming from an oil well often include a mixture of petroleum, connate water and hydrocarbon gas. In order to prepare the produced fluids for handling, i.e., transportation of the petroleum and gas and disposal of the water, the mixture must be separated into separate components. Since gas in most instances will readily separate from the mixture under conditions prevaling at the surface, the principal problem is separating the produced water from the oil. Water and oil, of course, have different densities and will gravity-separate from each other if left standing long enough. However, this requires a great deal of storage space, which can be very undesirable.
Many types of wash tanks have been used heretofore to separate the oil from water. These tanks have used heat, chemicals and baffles to promote separation of the oil and water. The tanks use various arrangements to assist separation of the two fluids so that the oil may be withdrawn from the top of the tank and water withdrawn from the bottom of the tank.
A baffled wash tank is described in copending application Ser. No. 753,047, now U.S. Pat. No. 4,064,054, issued Dec. 20, 1977. As there described, baffle sections are connected across the tank to prevent channeling of the oil-water mixture and thus to promote separation of oil and water. Each baffle section extends completely across the tank. The baffle section includes a perpendicular solid portion extending from above the inlet for the oil-water mixture in the tank to a position below the inlet for the oil-water mixture. The perpendicular solid portion of the baffle section is arranged substantially normal to the axis of flow of the oil-water mixture in a downward direction. The baffle section also includes an inclined slotted portion extending downwardly in the direction of flow from the lower edge of the perpendicular solid portion. The slotted portion utilizes rows of regularly spaced slots to assist in the separation of the oil and water. The above-described tank effectively promotes the separation of oil and water so as to permit a relatively small tank to be used, thus saving space and improving the transit time through the tank. However, it has been discovered that even more efficient operation can be achieved when the number of slots in the lower rows of slots in the inclined slotted portion of the baffle are increased in number over the number of slots in the upper row of slots.